//
// Created by Jisam on 13/09/2024 7:02 PM.
// Solution of  Cidoai的平均数对
//#pragma GCC optimize(3)
#include <bits/stdc++.h>

using namespace std;
#define coutn(x) cout << (x) << "\n"
#define endl "\n"
#define PSI pair<string,int>
#define PII pair<int,int>
#define PDI pair<double,int>
#define PDD pair<double,double>
#define VVI vector<vector<int>>
#define VI vector<int>
#define VS vector<string>
#define PQLI priority_queue<int, vector<int>, less<int>>
#define PQGI priority_queue<int, vector<int>, greater<int>>
#define code_by_jisam ios::sync_with_stdio(false),cin.tie(nullptr),cout.tie(nullptr)
typedef long long i64;
typedef unsigned u32;
typedef unsigned long long u64;
typedef __int128 i128;
int dx[] = {-1, 1, 0, 0, 1, 1, -1, -1,};
int dy[] = {0, 0, -1, 1, 1, -1, -1, 1,};
struct  node{
    int a,b;
};
void solution() {
    int n,k;
    cin >> n >> k;
    vector<node> ve(n);
    for(int i = 0 ; i < n ; i ++)
    {
        cin >> ve[i].a >> ve[i].b;
    }
    sort(ve.begin(),ve.end(),[&](node n1 ,node n2){return n1.b < n2.b;});
    i64 suma = 0, sumb = 0,cnt = 0;
    i64 ans = 0;
    int fast = 0 , slow = 0;

    while(fast < n)
    {
        if(sumb <= k * cnt){
            cnt ++;
            suma += ve[fast].a;
            sumb += ve[fast].b;
            fast ++;
        }else{
            suma -= ve[slow].a;
            sumb -= ve[slow].b;
            slow ++;
        }
        ans = max(ans,suma);
    }
    coutn(ans);
}

int main() {
    code_by_jisam;
    i64 T = 1;
//    cin >> T;
    while (T--) {
        solution();
    }
    return 0;
}